1. Field of the Invention
The present invention relates to an insertion device for inserting a deformable intraocular lens into the eye. Examples of such a deformable intraocular lens include a deformable intraocular lens that is inserted into the eye in place of the natural lens when the latter is physically extracted because of cataracts, and a vision correction lens that is inserted into the eye for the sole purpose of vision correction.
2. Description of the Related Art
Implantation of an intraocular lens for treating cataract has been widely performed since 1949, when Ridley implanted for the first time an artificial lens; i.e., an intraocular lens, into the human eye in place of an opaqued natural lens during cataract surgery.
As disclosed in Japanese Patent Application Laid-Open (kokai) No. 58-146346, there have been invented improved intraocular lenses which can be inserted into the eye through a small incision formed in the eyeball. In one of the improved intraocular lenses, at least an optical portion is made of a deformable elastic material having a predetermined memory characteristic. In another improved intraocular lens, at least an optical portion is made of an elastic material having a predetermined memory characteristic, and there are provided supports which are made of a material different from that of the optical portion and are adapted to support the optical portion within the eye.
Moreover, as disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 4-212350, the assignee of the present invention has proposed improved insertion devices. By use of these devices, the optical portion of an intraocular lens is compressed, rolled, bent, stretched, or folded so as to reduce its exterior size, thereby enabling the intraocular lens to be inserted into the eye through a small incision formed in the eyeball. These insertion devices facilitate an operation for implanting an intraocular lens into the eye.
FIG. 16 and FIGS. 17A and 17B show the conventional deformable intraocular lenses. The deformable intraocular lens 1 shown in FIG. 16 is composed of a circular optical portion 2 and two symmetrically disposed supports 3. The circular optical portion 2 is made of an elastic material having predetermined memory characteristics. The supports 3 are made of a material different from that of the optical portion 2, and bases 3a of the supports 3 are embedded in the peripheral region of the optical portion 2 for fixing, while wire-shaped tails 3b of the supports are curved. The deformable intraocular lens 1 shown FIGS. 17A and 17B is composed of a circular optical portion 2 and a pair of thin plate-shaped support portions 4 that are integral with the optical portion 2. The optical portion 2, like the optical portion 2 shown in FIG. 16, is made of an elastic material having predetermined memory characteristics. The support portions 4 are projected from the periphery of the optical port 2 in opposite directions.
FIG. 18 is a partially cutaway perspective view of a conventional insertion device for folding and deforming the above-described intraocular lens into a smaller size and for inserting the lens into the eye via an insertion tube.
FIG. 19 is an enlarged perspective view of the insertion tube used in the insertion device; FIG. 20 is an enlarged perspective view of an insertion end portion of the insertion tube; FIG. 21 is a cross sectional view taken along line 21—21 of FIG. 20; and FIG. 22 is an enlarged sectional view showing operation of the insertion end portion of the insertion tube used in the insertion device.
In FIG. 18, reference numeral 11 denotes a device body; 12 denotes a push rod; 13 denotes a male-thread shaft; and 14 denotes a push-out mechanism.
Reference numeral 18 denotes an enclosing member. As shown in an enlarged manner in FIG. 19, the enclosing member 18 is provided with a lens receiving section 16 having a hinge portion 15; and an insertion tube 17 projects from the front end of the lens receiving section 16. A tip end portion 17a of the insertion tube 17 has an axially extending slit 17b. The lens receiving section 16 is constituted by a stationary half sleeve 19 and a movable half sleeve 20 whose lower edge portions are connected together by means of the hinge portion 15. Stationary and movable press plates 21 and 22 project from the stationary and movable half sleeves 19 and 20, respectively.
The conventional insertion device having the above-described structure is used as follows. The intraocular lens 1 is placed on the lens receiving section 16 of the enclosing member 18 and is folded into a smaller size before being loaded onto the insertion device body.
Upon completion of loading of the intraocular lens 1, the male-thread shaft 13 of the intraocular-lens insertion device is rotated in order to screw-feed the push rod 12. As a result, a process of inserting the intraocular lens into the eye starts.
The intraocular lens 1 is pushed forward gradually by the tip end of the push rode 12. When the intraocular lens 1 reaches the insertion end portion 17a of the insertion tube 17, the axially extending slit 17b of the insertion end portion 17a opens gradually. As a result, stresses in the optical portion 2 of the intraocular lens 1, which was completely folded at a base end side 17c of the insertion tube 17, are released gradually at the insertion end portion 17a. Subsequently, the intraocular lens 1 is inserted into the eye from an open end 17d. 
During such insertion operation, the slit 17b holds the optical portion 2 of the intraocular lens 1 while sandwiching it, to thereby prevent abrupt discharge of the intraocular lens 1 into the eye. In addition, although the slit 17b releases stresses from the intraocular lens 1, the intraocular lens 1 is retained at the insertion end portion 17a, because cut surfaces located above and below the slit 17b hold the intraocular lens 1 from both sides thereof. Moreover, the slit 17b can control insertion speed of the intraocular lens 1 to match advancement speed of the push rod 12.
<Problems to be Solved by a First Aspect of the Invention>
However, since the insertion tube of the insertion device has no means for restricting rotation of the intraocular lens about the center axis of the insertion tube when the intraocular lens is pushed axially after being folded, as shown by an imaginary line in FIG. 22, the intraocular lens 1 may rotate in the circumferential direction of the inner wall surface of the insertion tube 17.
As a result, the positional relation between the slit provided at the tip end of the insertion tube and the folded intraocular lens changes, thereby making it impossible for an operator to eject the intraocular lens from the tip end of the insertion tube in desired conditions. Therefore, insertion direction and insertion speed of the intraocular lens are difficult to control with stability and high reproducibility, and therefore, operation of implanting an intraocular lens requires a high level of skill.
<Problems to be Solved by a Second Aspect of the Invention>
Moreover, the above-described conventional insertion devices have the following drawbacks.
The entire portion of the insertion tube, from the based end portion to the tip end portion, is formed of the same material, which is sufficiently strong to prevent the insertion tube from being broken by a lens moved through the insertion tube. Therefore, in the case in which the frictional resistance between the lens and the insertion tube is small, stress generated during deformation are released at a time when the lens is ejected from the tip end of the insertion tube into the eye, so that the lens flies out into the eye, possibly damaging the tissue within the eye.
In order to solve such a problem, insertion devices having a stress release structure have been proposed. One example of such a stress release structure is a slit which is formed to extend from the tip end of the insertion tube toward the base end portion thereof in order to gradually release stresses of a lens, and through which the lens is inserted into the eye.
Another example of such a stress release structure is a slant cut portion which is formed by obliquely cutting the insertion tube from the tip end of the insertion tube toward the base end portion thereof. The slant cut portion can release stresses gradually to thereby prevent flying out of a lens into the eye, which would otherwise occur upon sudden release of stress.
However, when a long slit extending from the vicinity of the base end to the tip end of the insertion tube is formed, or the angle of the slant cut portion is decreased in order to increase the length of the cut portion, to thereby release stresses more gently and thus enhance safety, the slit or cut portion faces the intraocular tissues in the vicinity of an incision. In this case, when the lens is inserted into the eye, the lens may come into contact with the tissue and damage it.